JP-A-2005-288770 describes an ink-jet printing device in which a sub-tank containing ink to be supplied to a print head is partitioned vertically by a ventilation film, a part below the ventilation film serves as an ink chamber containing ink, and a part above the ventilation film serves as an air chamber to which air in the ink chamber is discharged. The air chamber is connected to a deaeration pump with a valve interposed therebetween, and the air in the air chamber and the ink chamber is discharged externally by actuating the deaeration pump with the valve opened to suction the air in the air chamber. By closing the valve after suctioning the air in the air chamber by actuating the deaeration pump, the air chamber is maintained in reduced pressure and then the air flowing in the ink chamber is discharged to the air chamber due to the reduced pressure of the air chamber. Accordingly, it is possible to prevent the air from flowing into the print head together with the ink at the time of supplying the ink from the ink chamber to the print head.
In the ink-jet printing device described in JP-A-2005-288770, when the air in the ink chamber is discharged to the air chamber, the ink in the ink chamber and the print head communicating with the ink chamber varies in pressure and thus meniscuses of nozzles vibrate or the like. Accordingly, when the ink is ejected from the print head in this state, an ink ejection characteristic may vary. However, when the air chamber is maintained in reduced pressure, the air reaching the vicinity of the ventilation film is discharged from the ink chamber to the air chamber, and therefore, it can not be detected when the air is discharged. As a result, the ink may be ejected from the nozzles at the same time when air is being discharged from the ink chamber to the air chamber.